Irradiation systems are used for irradiating medical devices, foodstuffs, food utensils, as well as other goods such as cosmetics, waste products and the like. Typically high energy ionizing radiation is used as the radiation source, for example gamma radiation, X-ray, electron beam, or the like. The source, in the case of a radioisotope, is typically maintained beneath the irradiation chamber within a pool when not in use, and raised into position as required. Articles of interest are placed upon pallets, or loaded into unique carrier trays, and these pallets or carriers are conveyed past the radiation source in order to expose the contents therein.
It is well known within the art, that even exposure of the article to the source will provide a more optimum irradiation. In this regard, the dose-uniformity ratio (DUR), which is the ratio between the maximum and minimum dose that a product receives, is used as a measure for exposure uniformity. In order to optimize the DUR, several conveyor-track assembly, and their relationship with radiation source locations have been considered.
Many prior art irradiators utilize conveyors in order to move a product laden carrier past an radiation source, for example U.S. Pat. Nos. 5,396,074, 5,001,352, 4,866,281, 4,852,138, 4,561,358, 4,481,652, 3,676,675 or U.S. Pat. No. 3,564,241. These irradiators utilize a source-overlapping-product configuration, and operate with a low efficiency of source utilization. Furthermore, these systems necessitate the use of many moving mechanical parts within the irradiation chamber, yet the environment within the irradiation chamber is hard on many plastics and metals. Such designs are therefore prone to repeated failures that require full shutdown of the irradiator for repair. Similarly, other transport systems, (U.S. Pat. Nos. 4,066,907, 4,018,348) use turntables coupled with conveyor systems to expose a product to a source. These systems also comprises many moving parts within the radiation chamber, and necessitate substantial product handling within the irradiation chamber. Furthermore, all of the above irradiators require extensive unpackaging and repackaging of the product from a pallet to the carrier, and following radiation treatment back, onto the pallet for shipping.
Other irradiators have adopted an alternate transport system with which to move a product past a source. In U.S. Pat. No. 5,396,074 there is disclosed a facility for irradiating foods and medical devices using an electron beam as the radiation source. An overhead transport conveyor is used to suspend article carriers to permit their movement around a track and to bring these carriers in front of the radiation source. The suspended article carriers are capable of rotating upon their vertical axes which permits radiation of two sides of a product disposed within the article carrier. This design permits exposure of both sides of the article carrier to the radiation source. However, radiation by electron beam may result in a poor depth of penetration in medium to high density products (i.e. over about 0.4 g/cc), and extensive repackaging is required in order for such products to be treated effectively with a low resulting DUR. This type of irradiator therefore has a limited use. A similar conveying system is found in U.S. Pat. No. 4,481,652 and U.S. Pat. No. 3,673,409, with carriers suspended from a monorail-type track. This system uses cam-catch members that are powered in order to push the product carriers through the labyrinth path before the gamma radiation source.
U.S. Pat. No. 5,400,382 is directed to irradiating products, located on pallets moved on shuttle cars, with gamma rays. The shuttle cars move the pallets into the region of the gamma source, on a series of parallel tracks, and the pallets are transferred from track to track so that each side of the object being irradiated is exposed. Again, with such a design there are many moving parts located within the irradiation chamber thereby minimizing access for maintenance and repair. Furthermore, these irradiators use a source-overlapping-product configuration which results in a low efficiency of radiation utilization.
Several irradiator designs do not require the introduction of the source into the irradiation chamber, rather the product is lowered into the pool surrounding the source. For example, U.S. Pat. No. 3,676,675 is directed to a subterranean production irradiator with a product conveyor system comprising an endless chain and sprockets arranged to permit movement of specialized product carriers past an radiation source. The product carriers are hung from the chain, and pass over and under the source in a sinusoidal path. A similar approach is disclosed in U.S. Pat. No. 4,760,264; 4,908,221; 5,008,550 which incorporates a water-tight duct system through which carriers are passed. The conveyor system comprises a continuous chain in order to move the product through the duct system. In all of these designs, the speed of the conveyor effects all carriers attached to the conveyor, any variation in speed affects all product carriers at the same time throughout the ductwork. Any mechanical problem localized within the subterranean irradiation chamber is also very difficult to repair, and this is complicated by the fact that the source can not be easily removed from the irradiation chamber resulting in time consuming maintenance or repair procedures. Due to the types of carriers employed, extensive product handling in order to load and unload the carriers from, and to, a pallet is required.
U.S. Pat. No. 4,561,358 is directed to an apparatus for conveying elongated articles through an radiation beam. The conveying means comprises two overhead tracks, and a guide that associates with, but is located below the carrier to direct the orientation of the article and permit both sides of the articles to be exposed to the radiation source. U.S. Pat. No. 3,564,241 is directed to an irradiation apparatus comprising a continuous horizontal track to form a single path around a radiation source.
U.S. Pat. No. 4,066,907 discloses the use of a turntable with several levels that circumscribes a vertically placed source. This configuration permits the partial exposure of the top and bottom of the product to the source. The product is moved onto the turntable by a goods handling appliance, such as a fork lift coupled with a telescopic table. The same goods handler is also used to transfer product between levels of the turntable in order to permit exposure of the sides and a portion of the top and bottom of the product to the source. All of this material handling takes place within the irradiation chamber. Due to the harsh environment within the irradiation chamber, routine maintenance requires shutdown of the irradiator. The carriers used within each irradiators also require extensive product handling and repackaging in order to load and unload the carriers. These irradiators also employ a source-overlapping-product configuration which results in a low efficiency of radiation utilization.
Several problems exist with most prior art product irradiators. Many designs require considerable carrier handling within the irradiation chamber either to complete a pass around the source, or to effect a change in the level of turntable or conveyor. Furthermore, several designs require extensive carrier loading and unloading before an after exposure to the source, due to the use of specialized carrier trays used for product radiation. This is especially true if the product is orientation-sensitive and must be loaded in a specific manner prior to treatment. Furthermore, carriers of the prior art do not easily permit variable product heights to be easily loaded or continuously passed around the source. In general, product packaging limitations result in limited flexibility of irradiator use.
As a result of the required carrier handling devices and associated mechanism, as well as track or conveyor configurations, or carrier designs, there is much support or structure between the source and product within many prior art irradiators. This structure attenuates the radiation emitted from the source and reduces the efficiency of radiation utilization within the irradiator. Furthermore, many prior art irradiators adopt a source-overlapping-product configuration and this further results in an a lower efficiency of radiation utilization.
The environment within the irradiation chamber is also harsh on components that are subject to repeated radiation exposure including the product carriers, transfer mechanisms, pulleys, bearings and track assemblies. For example, gamma radiation, through cross linking, degrades carbon based, and related materials, including lubricants, plastics, non-metallic seals and the like. Furthermore, when the surrounding air is irradiated, ozone is produced which is a strong oxidant that corrodes ferric metals. Therefor, any suitable product irradiator design should consider minimizing the number of moving parts within the irradiation chamber, as well as permitting the easy removal of components repeatedly exposed to radiation in order to minimize downtime of the irradiator.
The product irradiator of the present invention sets out to overcome the deficiencies identified within the art, and ensures an optional dose uniformity ratio (DUR). In addition, the number of moving parts exposed to the irradiation chamber environment has been reduced in order to minimize effects of radiation and ozone on the components. Furthermore, most of the moving parts spend a substantial portion of time outside the irradiation chamber, which extend their use and reduces maintenance, and provides for easy access for repair and replacement. The design of the present invention also permits easy removal of components from the irradiation chamber for repair thereby minimizing down time of the product irradiator.
The carriers of the product irradiator of the present invention are designed to minimize or eliminate product repackaging, and ensure that palleted goods can be placed onto appropriately sized carriers and, following treatment, can be easily repalleted. A result of easy carrier loading and unloading results in greater product throughput. The product irradiator of the present invention also incorporates a carrier that can be used with orientation-sensitive goods, and readily accommodates goods that vary in height.
Another problem associated with prior art irradiators, is that the carriers can not accommodate wide variations in product size since the carriers used are of a fixed dimension, and the track, or conveyor, assemblies are fixed at preset distances from the source. Typically, the DUR for a product is specified and the packing of product within the carrier is altered to achieve the desired DUR specification for a given pass. Often such packing results in low packing efficiencies within the carrier, which translates into reduced product throughput. Furthermore, non-optimal packing also leads to low utilization efficiencies of the source. The design of the present invention provides for an adjustable carrier height with respect to the track and this feature accommodates a wide range of product dimension, while maintaining the DUR within required specified ranges. This means that, instead of manually arranging product loading to meet the required specified DUR for a given product class, the irradiator design of the present invention allows the operator to automatically achieve the desired DUR while also maximizing throughput.
The irradiator of the present invention also provides for greatly reduced product support structure between the source and product thereby reducing attenuation and increasing the efficiency of source utilization. Furthermore, the irradiator may be used in either a product-overlapping-source, or a source-overlapping-product configuration as required.
The product irradiator of the present invention also involves the use of a continuous track with level-changing portion which provides a novel path for a product laden tray to circumscribe a source through a variety of heights, and from a variety of directions. Such a path results in an optimal DUR.